This invention generally relates to apparatus for the preparation of a fluid sample upon a slide for microscopic analysis, and more particularly, to improved apparatus for supporting the slide and spreading the sample thereon.
Prior art devices such as those described in U.S. Pat. No. 4,359,013 have employed a base on which a slide to be stained is supported flat on a support surface thereof. A spreader is manually movable linearly relative to the base and engaging the surface of the slide with appreciable downward force so that the fluid sample can be spread over the slide to form a so-called "monolayer" of the sample. The spreader is intended to be disposable after each use thereof. Typically, a blood sample is spread into a monocellular layer on the slide which can then be microscopically examined for blood cell differential screening.
Several deficiencies exist in such prior art devices. As structured, the spreader frictionally engaged said support surface so that it formed grooves or ruts in the support surface of the base after multitudinous passes. Eventually, irregularities in the path of the movement of the spreader relative to the slide actually interfered with uniformity of spreading of the sample and thereby prevented achieving the desired monocellular layer consistently with the same base which was not intended to be disposable. Also, the base tended to deform or flex downwardly because of the necessity to press downwardly on the spreader when making the monolayer. This deformation or flexing contributed to breakage of the slides on occassion as well as possible non-uniformity in monolayer spread of the sample on the slide.
In the referenced application Serial No. 434,378, the sample spreader rides entirely upon the slide in a linear movement for preparing the sample smear. Therefore, grooving in the slide support surface of the base is avoided. However, the use of a slide having a textured or "frosted" end area to accept written identification has sometimes led to interruption of the smear when the legs of the spreader arrive at the abrupt line of transition between the smooth glass and the frosted end area. The resulting interruption or "banding" may result in an insufficient extent of the smear for proper microscopic examination by automatic instruments. Such smear banding is eliminated by the apparatus of the described invention herein.